Aqueous coating composition

Abstract

A water based coating composition prepared by dispersing by use of a suspension stabilizer into water a film-forming component of 30 to 90 percent by weight of (a) a blocked isocyanate compound having at least two blocked isocyanate groups in one molecule and a number average molecular weight of 150 to 5000, and 10 to 70 percent by weight of (b) a methylol group or methylol ether group-containing aminoplast crosslinking agent. The film-forming component can be dispersed into water in the form of a mean particle size by a 50 percent cumulative particle size of 0.1 to 10 μm. The coating film-forming component in the water based coating composition is very stable in water and is particularly suitable for the water-based coating composition. The coating film-forming component scarcely shows solubility and dispersibility into water by itself, but dispersion thereof with the suspension stabilizer shows excellent dispersion stability. The water based coating composition is useful, for example, as a topcoat for automobiles.

What is claimed is:  
     
         1 . A water based coating composition prepared by dispersing by use of a suspension stabilizer into water a film-forming component comprising 30 to 90% by weight of (a) a blocked isocyanate compound having at least two blocked isocyanate groups in one molecule and a number average molecular weight of 150 to 5000, and 10 to 70% by weight of (b) a methylol group or methylol ether group-containing aminoplast crosslinking agent, so that the film-forming component may be dispersed into water in the form of a mean particle size by a 50% cumulative particle size of 0.1 to 10 μm.  
     
     
         2 . A water based coating composition as claimed in  claim 1 , wherein a blocking agent used in the blocked isocyanate compound is a monohydric alcohol having C 1-20  alkyl group.  
     
     
         3 . A water based coating composition as claimed in  claim 1  or  2 , wherein the isocyanate used in the blocked isocyanate compound is a polyisocyanate derived from hexamethylene diisocyanate.  
     
     
         4 . A water based coating composition as claimed in any one of  claims 1  to  3 , wherein the aminoplast crosslinking agent is a melamine resin.  
     
     
         5 . A water based coating composition as claimed in any one of  claims 1  to  4 , wherein the suspension stabilizer includes ones prepared by neutralizing an acrylic resin having a hydroxy value of 10 to 300 mgKOH/g, an acid value of 10 to 300 mgKOH/g and a weight average molecular weight of 5000 to 100000 with a basic substance.  
     
     
         6 . A water based coating composition as claimed in any one of  claims 1  to  5 , wherein the suspension stabilizer is in the range of 0.1 to 40 parts by weight per 100 parts by weight of the coating film-forming component in the water based coating composition.  
     
     
         7 . A water based coating composition as claimed in any one of  claims 1  to  6 , wherein the water based coating composition contains a volatile organic compound in an amount of 179.7 kg/m 3  or less.  
     
     
         8 . A water based coating composition as claimed in any one of  claims 1  to  7 , wherein the water based coating composition is a clear coating composition.  
     
     
         9 . A water based coating composition as claimed in any one or  claims 1  to  8 , wherein the water based coating composition is used as a topcoat for the automobile.  
     
     
         10 . A water based coating composition as claimed in any one of  claims 1  to  9 , wherein the water based coating composition is coated onto a water based base coat by a wet-on-wet coating.